Abstract: This invention relates to a derail assembly used in the railroad industry for derailing a wheel of an undesirably moving railed vehicle. The invention particularly relates to derailing a moving locomotive having a pilot at the front of the locomotive. The derail may be a single ended derail or a double ended derail. The derail includes a rigid derail plate which is in direct contact with the upper surface of the rail. An upright derail bar is securely mounted on the derail plate and the derail bar is angled outwardly for engaging a wheel of the locomotive or other railway car when moving undesirably for causing a desired derailment. The second derail bar may be provided in the case of a double ended derail. The derail includes longitudinally spaced rigid hooks at opposite ends of the derail to secure one side of the derail to the rail. The opposite side has a clamp mounted on the derail for securing the derail to the rail.